Biosensing is under current research and development for a wide range of applications in the field of functional genomics and molecular diagnostics, for example. One technique uses fluorescent labels, which are optically detected with laser scanners. However, the required instrumentation needs to be reduced in size and cost to realize a hand-held device. Preferred sensing systems have high sensitivity, rapid response, portability, and low cost, preferably not requiring DNA amplification process. In addition, the biosensing system is desired to be compatible with CMOS processing, and can be easily integrated with a CMOS chip to form a lab-on-a-chip system.
Biosensing using magnetic microarrays has been proposed. The basic methodology of such a magnetic microarray is that a single-stranded DNA with a known sequence is immobilized (bound) on the sensor surface through a sulfur-Au linkage. Meanwhile, a tagging process using single-domain high-moment magnetic nanoparticles as tags are attached to targeted DNA fragments. When the tagged DNA fragments are selectively captured by complementary DNA probes that are attached to the sensors, the stray field of the magnetic nanoparticles is read out by the magnetic sensors. A giant magnetoresistive spin-valves or magnetic tunnel junction is used for magnetic field sensing.
One problem with these biosensors is that the sensing suffers from a large 1/f noise coming from the sensors themselves and from the MOS switches. There is a need for a biosensor that reduces 1/f noise without increasing the complexity of the system by implementing a frequency modulation scheme.